This is fragile code! There are actually *two* classes that do almost
precisely the same thing, they are:

- ImplFontMetric, and
- ImplFontMetricData

They both have much in common, including their class name, and even
most of their functionality. In fact, they both have common accessor
functions. When I look at the code, it looks like OutputDevice is
actually given an ImplFontMetricData object, which it then uses to
populate an ImplFontMetric object...

Basically, I'm going to merge these classes. To do so, I'm going to
do the following:

Step 1: Implement accessor functions for ImplFontMetric and FontMetric
        (then remove the friendship of this class to OutputDevice!)
Step 2: Write a unit test for each accessor function in ImplFontMetric
Step 3: Ensure that ImplFontMetric and ImplFontMetricData use some
        sort of smart pointer (probably an intrusive_ptr like I did
        ages ago with FontCharMap)
Step 4: Merge the two classes together once their class interfaces
        are the same and I am satisfied they do the same thing
Step 5: Find all instances of inefficient usage - for instance, I can
        do away with the code that copies the ImplFontMetricData
        attributes into an ImplFontMetric object.

Change-Id: I07c1cb848774b130fa2ca60b51da53e07754dd00
Reviewed-on: https://gerrit.libreoffice.org/21399Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>